The invention concerns a petroleum product and a process for the production of said petroleum product which can form part of a blend for an internal combustion engine fuel, and to the product obtained by the process. Gas oils currently on the market, either as internal combustion engine fuels or as a domestic fuel, are most often refined products which contain about 0.3% of sulphur (expressed as weight of sulphur). They are normally produced by hydrofining a feedstock which may be a straight run distillate of a crude petroleum or from a particular crude petroleum treatment (for example pyrolysis or distillation followed by pyrolysis of the fraction recovered during distillation, or thermal or catalytic cracking), generally containing at least 0.8% by weight of sulphur.
The prior art is illustrated in U.S. Pat. No. 5,059,303, which describes a process for stabilising hydrocarbon fractions (syncrude oils) which are very sensitive to light, heat and oxygen, for example. Those hydrocarbons are generally shale oils whose principal characteristic is their high nitrogen compound content, particularly basic nitrogen compounds (nitrogen content of at least 1% to 3%), which renders them unacceptable as feeds for conventional treatment processes. Those particular hydrocarbon fractions must, therefore, be pretreated before use, using severe hydrotreatment conditions.
Some industrial countries set standards regarding sulphur content and cetane index, or will shortly limit them. These standards are becoming more strict, particularly for gas oils for use as motor fuels. Thus in France, in particular from 1995, the sulphur content of gas oils will be set at a maximum of 0.05% by weight (500 ppm) while gas oils which conform to current standards can have a sulphur content of up to 0.3%.
Gas oils used in France as internal combustion engine fuels must currently have a cetane index of at least 48 and gas oils used as a domestic fuel must have a cetane index of at least 40. These standards can be expected to become stricter in the near future, in particular those regarding gas oils used as motor fuel.
Further, given the diversity of feeds to be treated (crudes of different origins, from visbreaking, coking, hydroconversion, distillation or catalytic cracking) to produce a gas oil, a flexible process should be available to the refiner which can adapt the products formed to the demand and comply with future specifications regarding sulphur levels, nitrogen levels, cetane index, color and aromatic content.
All the existing processes, such as hydrodearormatisation or hydrocracking, which produce petroleum products with a low sulphur content and a relatively high cetane index, use large quantities of hydrogen. Hydrodearomatisation of a straight run feed with distillation intervals (ASTM D86) of 180.degree. C.&lt;T 5%&lt;300.degree. C., 260.degree. C.&lt;T 50%&lt;350, 350.degree. C.&lt;T 95%&lt;460.degree. C., uses 0.6 to 1.1% of hydrogen with respect to the feed, while hydrocracking requires more than 2% of hydrogen with respect to the feed. Thus the hydrogen feed in a refinery, generally the catalytic reforming unit, is likely to become inadequate as regards the increasing severity of gas oil standards which will necessitate an increase in hydrotreatment.
Further, the current processes produce a petroleum product with a cetane index which does not exceed 63, this latter only being obtainable at the cost of hydrogenating the aromatic hydrocarbons in the feed, a reaction which consumes hydrogen.
The refiner therefore needs a process which can produce a petroleum product which can comply with the various standards which will come into force in the near future, from 1995 in the case of sulphur content. It is also desirable to be able to produce a petroleum product with as little odor as possible.